There are several applications for laser radiation projected to form a line of light on a target. Early versions of such line-projection apparatus for diode-lasers were found in bar-code readers and the like. Here, however, uniformity of illumination along the line was at most a secondary consideration.
Later versions of diode-laser line projection apparatus were developed for spatial light modulators (SLMs) in laser printers, image projectors, and the like. Here, power in the line of light was not required to be very high, and could be delivered by a simple one-dimensional laser array, commonly referred to as a diode-laser bar. Uniformity of illumination along the line of light in these applications is important. An “ideal” line of radiation requires a Gaussian intensity distribution of intensity in the width of the line and a uniform or “flat-top” distribution along the length of the line. This uniformity requirement encouraged the invention of projection optics that would provide adequate uniformity. Examples of such projection optics are described in U.S. Pat. No. 6,773,142, U.S. Pat. No. 7,016,393, U.S. Pat. No. 7,265,908, and U.S. Pat. No. 7,355,800, all of which are assigned to the assignee of the present invention.
A recent application for projecting a spot of a predetermined length-to-width ratio is laser cladding. In laser cladding, a durable protective layer is formed on a surface by depositing the layer material in powder form on a surface while simultaneously irradiating the powder covered surface with laser radiation to melt the powder which flows, then hardens on the surface to form the layer. The powder and radiation source moves over the surface while the layer is being formed. More laser power provides that a faster layer-forming speed can be achieved for any given spot dimension. A typical spot would have a width of about 1.0 mm and length between about 3.0 mm and 30.0 mm, with between about 2 and 8 kilowatts (kW) total power delivered into the spot.
The spot would preferably have Gaussian distribution of intensity in the spot width, and a uniform (“flat top”) distribution in the spot length. Depending on the optical efficiency of the illuminating apparatus, this would require a diode-laser source with a total power possibly in excess of about 3 kW. As the power available from a typical multimode diode-laser bar is only on the order of 70 Watts (W), such a 3 kW-source would require about 50 diode-laser bars. In order to provide 7 kW, 100 diode-laser bars would be required.
In many instances a user of cladding apparatus may have a requirement for different spot-shapes for different cladding operations, and possibly even for different power in a spot having a fixed size. At present this requires a different projector for each different spot shape. It would be convenient and cost effective to have one projector capable of projecting all of the necessary different spot shapes, preferably with variable power. The spots should be projectable at the same working distance in the projector.